Flesh out the package kit solver API quite a bit more

* Reorganize things a bit:
  - BSolver is now an abstract base class.
  - A libsolv based implementation, LibsolvSolver, lives in a new
    add-on, which is loaded lazily.
  - Get rid of libpackage_solver. Save for LibsolvSolver everything
    is moved to libpackage.
  - This is a nicer solution for the cyclic dependency caused by
    libsolv (libsolvext to be precise) using the package kit for
    reading repositories and package files.
* Add a solver result data structure and and an accessor the solver.
* Add problem reporting support to the solver. There aren't data
  structures for the problem solutions yet and support for selecting
  solutions and re-solving is missing as well.

headers/os/package/solver/Solver.h

@@ -13,30 +13,42 @@ namespace BPackageKit {
 
 
 class BSolverPackageSpecifierList;
+class BSolverProblem;
 class BSolverRepository;
+class BSolverResult;
 
 
 class BSolver {
 public:
-								BSolver();
-								~BSolver();
+	virtual						~BSolver();
 
-			status_t			Init();
+	static	status_t			Create(BSolver*& _solver);
 
-			status_t			AddRepository(BSolverRepository* repository);
+	virtual	status_t			Init() = 0;
 
-			status_t			Install(
+	virtual	status_t			AddRepository(
+									BSolverRepository* repository) = 0;
+
+	virtual	status_t			Install(
 									const BSolverPackageSpecifierList&
-										packages);
+										packages) = 0;
 
-private:
-			class Implementation;
+			bool				HasProblems() const
+									{ return CountProblems() > 0; }
+	virtual	int32				CountProblems() const = 0;
+	virtual	BSolverProblem*		ProblemAt(int32 index) const = 0;
 
-private:
-			Implementation*		fImplementation;
+	virtual	status_t			GetResult(BSolverResult& _result) = 0;
+
+protected:
+								BSolver();
 };
 
 
+// function exported by the libsolv based add-on
+extern "C" BSolver* create_solver();
+
+
 }	// namespace BPackageKit